This invention relates generally to highly efficient, radiant power transferring, light engines and, in particular, to projection display systems, fiber-optic illumination systems, and to the design optimization of related components.
Many applications of light, or more broadly, coherent and incoherent electromagnetic energy, require a physical separation between the locations of light generation and the locations of its use, i.e. target locations. Together all light usage locations of interest form a target T. In the same manner, all energy emission locations of interest form a source S. Such electromagnetic energy radiating sources can be operated continuously or pulsed, can be incoherent, coherent or partially coherent and/or a combination thereof. They can be energized by AC or DC currents, by microwave heating, by electromagnetic radiation means using energy in similar and/or different wavelength regions, by chemical means, and by many other sources of energy. Depending on the distributions of the respective location of interest they can be characterized either as surface, volume, as surface and volume type source S and target T.
A given target T usually has some associated formatting requirements on the light beam used to illuminate it. Further, the spectral, spatial and angular emission energy density function of a source S, is in general different from the spectral, spatial and angular light acceptance function of a given target T. Therefore, for best energy coupling between a given source S and a given target T, the associated target illumination beam has typically to be reformatted to increase the delivery efficiency of collectable light that is also usable by the target. Examples of common formatting requirements for a target illumination beam are restrictions for DE its cross sectional shape and size near the respective collection aperture, its spatial intensity distribution, its minimum and maximum intensity level, its maximum incident angle dependent on a preferred azimuth direction, its local energy propagation direction, its spectral energy content and spectral intensity distribution, etc. Further, in many types of illumination systems, selected internal optical components choices (for example, a Color Wheel (CW), a Light Valve (LV), a Light Guide (LG), a Polarization Conversion System (PCS), a color cube combiner (CQC), an Anamorphic Beam Converter (ABC), etc.) and/or component layout constraint (input and output coupling of a LV, maximum height of a component, etc) effect the maximum light delivery efficiency. These design constraint and/or throughput limiting components can effectively also be interpreted as effective or intermediate targets Txe2x80x2.
Only those light rays that fulfill the formatting requirements of a given target T are useful for the illumination of the target T. The rest of the light rays, incident either on the target T itself or its neighborhood, are typically wasted. Often these non-usable rays have to be stopped with masks and or spectral filters from reaching the target T or its surrounding space to prevent them from interfering with a particular target illumination application: for example, by causing an undesired overheating of the target object itself or reducing the image contrast in a projection display system. Often also selected color bands and/or polarization directions have to be attenuated to create a particular color balanced system with a chosen white point and color gamut and/or a well defined polarization state.
Thus, it is in general preferred that light (i.e., for the purpose of this invention, electromagnetic radiation of any wavelength) is captured from a source S and delivered to a target T be reformatted in such a manner that as much as possible of the light delivered to a given target is also useable by the target T.
A Light Engine (LE) is an apparatus that accomplishes the above described electromagnetic radiation power transfer and beam-formatting task. It is typically made up of multiple optical components that together have at least two or three major tasks. The first task is to collect light from a source S. The second task is to deliver some of the collected light to the target T. The third, and often optional, task is to reformat the light beam to enhance the usable content of the light delivered to the target T.
To facilitate an understanding of this invention, three subclasses of LE""s are defined: a Minimal Light Engine (MLE), a Light Guide Light Engine (LGLE) and an Anamorphic Beam Transformer Light Engine (ABTLE). A MLE is a special LE (or a portion of a more complex LE) that collects light emitted from the emission surface ESs or emission volume EVS of a source S and concentrates it inside a volume EVSxe2x80x2. This volume EVSxe2x80x2 can be interpreted as the emission volume of a secondary source Sxe2x80x2, also called emission source Sxe2x80x2, that illuminates either a target T directly or the collection aperture CA of a beam reformatting and/or remote transmission system of a related LE. A LGLE is another special LE where a MLE couples energy into at least one LG (for example for beam reformatting and/or remote energy transmission purposes) and where the input port of the respective LG collects light from the emission volume EVSxe2x80x2 of the respective MLE. The respective illumination target T is the exit port of the respective LG optionally combined with constraint for the spatial and/or angular extend of the exiting beam. An ABTLE is similar to a LGLE and uses at least one ABT for beam reformatting purposes. If the LG is also an ABT then a LE can be both a LGLE and an ABTLE.
The optical parameters called xc3xa9tendue E, xc3xa9tendue efficiency EE, throughput efficiency TE and delivery efficiency DE are important in better understanding this invention and are defined and discussed below. The xc3xa9tendue E is a measure of both the spatial and angular confinement of a light beam. The throughput TE and xc3xa9tendue efficiency EE are related parameters and measure in different ways how efficiently a given optical system reformats a given input beam compared to an ideal performing optical system. The delivery efficiency DE parameter measures both the fulfillment of the target formatting requirements and the throughput efficiency of a LE for a given target T, i.e. measured the amount of both collectable and usable light by a given target T.
This invention relates to both high efficient MLE, LGLE and ABTLE and where the respective input and output ports of the respective LG""s and/or ABT""s are preferably customized to the respective MLE and Target T to optimize the delivery efficiency of a given and constrained LE design.
The below referenced invention discloses embodiments that are satisfactory for the purposes for which they were intended and are in their entireties hereby expressly incorporated by reference into the present application for purposes including, but not limited to, indicating the background of this invention and illustrating the state of the prior art.
U.S. Pat. No. 5,491,765 to Matsumoto (1996) describes a typical LGLE design where a parabolic, sealed short arc reflector lamp, in combination with a focusing lens, is used to deliver collected energy to the entrance surface of a round fiber optic LG. Another related common, on-axis, prior art LGLE design uses an ellipsoidal mirror as Collection and Concentration System (CCS) of a lamp with a separate envelope. Both design families are of a non-imaging type and therefore result typically a low xc3xa9tendue efficiency EE. Thus, they achieve a high delivery efficiency DE only for large diameter fiber bundles having an input area ALin greater than  greater than AS with AS being the respective effective cross sectional area of the emission region of the source S.
U.S. Pat. No. 4,460,939 to Marakami et. all (1984) shows a LGLE which has a double concave reflector system as MLE and a sheet LG, thus creating spatial high output intensity uniformity, high delivery efficiency, but also low xc3xa9tendue efficiency since the collection xc3xa9tendue of the LG is much larger than that of the emission source. U.S. Pat. No. 5,574,328 to Okuchi (1996) discusses a MLE which has a double concave reflector forming a CCS with the source axis of a gas discharge arc lamp aligned co-linear with the optical axis of the CCS. The orientation of the light source and the astigmatic secondary focus in two orthogonal planes creates again a non-imaging type CCS system and thus reduces the xc3xa9tendue efficiency of that MLE. U.S. Pat. No. 5,491,620 to Winston et. all (1994) has a double concave reflector system as CCS for the MLE and a LG collecting the re-concentrated light. Since the maximum collection angle of most light guides is much below 90 deg, such a system has a low delivery efficiency for targets with a maximum acceptance angle of  less than  less than 90 deg. U.S. Pat. No. 5,842,767 to Rizkin et all (1998) shows an on-axis elliptical reflector with a hollow conical reflector as area and angle converter and an auxiliary retro-reflector. While this system is adequate for achieving higher coupling efficiency into larger diameter LG""s it is still of an non-imaging type and therefore does not maximize the xc3xa9tendue efficiency and the delivery efficiency for xc3xa9tendue limited targets.
Recent off-axis U.S. Pat. No. 5,414,600 to Strobl (the present inventor) et. al. (1995) and on-axis U.S. Pat. No. 5,509,095 to Baker et. al. (1996) are representative examples of prior art, quasi-imaging, peak intensity maximizing, fiber optic LGLE""s. They are typically used to illuminate very small diameter, round, single optical fibers or fiber bundles in conjunction with a short arc DC-type source. The off-axis LGLE can achieve higher delivery efficiency DE only for multi port outputs leading to complex beam combining optical systems and the on-axis LGLE has significant collection efficiency limitations for most practical higher NA LG.
The design and manufacturing limitations of the above mentioned basic types of prior art LGLE designs result often in lower delivery efficiencies and/or higher total system costs than are desirable under certain circumstances. This is particularly true for the cases, where the maximum acceptance (also called collection) xc3xa9tendue ETmax of a given or intermediate target T or Txe2x80x2 is of a similar magnitude than the characteristic emission xc3xa9tendue ES of the source S. Thus in order to fulfill the illumination demand of a given target, the lower delivery efficiencies of prior art LE""s typically require the usage of special sources that have a much lower emission xc3xa9tendue ES less than  less than ETmax, i.e. that have very small and very high intensity emission regions. Typically, DC or AC short plasma arc technology is being used to manufacture such high brightness and point-like emission sources. These short arc lamps are typically less efficient in their electrical to optical energy conversion than same type longer arc sources so that often higher wattage lamps have to be used to obtain a given target illumination level. Often the total systems cost is increased due to the additional requirements for an associated, higher wattage power supply and/or increased cooling and space requirements. In addition, the lifetime of such high brightness, point-like arc sources typically decreases with the increase of the lamp wattage for constant arc gaps and/or the shortening of the arc gap for constant electrical power level, thus resulting in higher overall system maintenance expenses.
Prior art Projection Light Engines (PLE""s), which are designed to illuminate a projection screen by illuminating first a LV, are even more complex and optically demanding than the above-discussed prior art LGLE""s. The selection of particular optical key components for a PLE often introduces additional design constraints. Typically, the LV is either directly or indirectly the most xc3xa9tendue limiting optical element of the respective PLE design. Due to the more limited optimization choices of the prior art PLE designs, an optical PLE designer has to balance screen uniformity, color gamut and white point with system brightness and mechanical packing constraints to achieve the best overall compromise. These design compromises lower the throughput-efficiency TE, xc3xa9tendue efficiency EE and/or delivery efficiency DE of a respective constrained PLE design.
U.S. Pat. No. 5,592,188 to Doherty (1997) describes a typical PLE for a single digital micro mirror device (DMD) type reflective LV. The respective MLE discussed in this patent is very similar to the one discussed in U.S. Pat. No. 5,491,765. However, instead of illuminating a LG, this system focuses the collected source energy onto a color wheel, which creates a time sequenced color beam. The color wheel is another key optical component that introduces additional constraints on the PLE design and is one of its major throughput efficiency limiter.
U.S. Pat. No. 5,442,414 to Janssen and Shimizu (1995) describes the use of an asymmetric mask that clips an illuminating beam in a special asymmetric manner so that the divergence angles xcex8LV(xcexa8) of the illumination beam have a predetermined function with respect to an azimuth angle xcexa8, that is measured against an optical preference axis of a DMD type LV. U.S. Pat. No. 5,098,184 to van den Brandt and Timmers (1992) describe lens array designs for the spatial beam intensity homogenization in a PLE that illuminates a liquid crystal type LV. These two improvements somewhat increase the delivery efficiency DE of the respective PLE by improving the formatting of the illumination beam to better match the formatting requirements of the LV with the inclusions of additional optical components. However, they achieve lower than possible delivery efficiency for xc3xa9tendue limited designs due to the lower xc3xa9tendue of efficiency of prior art PLE designs.
In order to increase the light output of a PLE for a given LV, several variations of the color wheel based, single LV, PLE design have been implemented. The goals of these designs is to reduce the high throughput losses ( greater than 70%) associated with the color wheel. For example, U.S. Pat. No. 5,528,318 to Janssen (1996) describes a single LV, PLE where the color wheel is replaced with a special scanning prism. By combining this scanning prism technology, with, when necessary, polarization conversion technology, in principle all the light emitted by a source S can be used to illuminate a single LV for the generation of color images. However, these beam reformatting enhancement technologies typically increase by a factor of 3-6 (6-12 for polarization dependent LV""s with PCS) the xc3xa9tendue of the LV""s illumination beam. This reduces the effective illumination area of the LV by a factor of 3-6 (or 6-12) which in general reduces coupling efficiency. Therefore, the scanning prism method in combination with the limits of prior art PLE design methods is currently beneficial only for larger area LV""s. The larger the area of the LV""s, i.e. the larger its maximum collection xc3xa9tendue, the less they depend on the xc3xa9tendue efficiency EE of a PLE to achieve a given projection screen brightness. However, larger LV""s also costs typically more to manufacture and require larger sized optics to steer the light beams, thus limiting thus far the advantages of these inventions.
Another method commonly used to increase the output of color PLE is to use multiple LV""s simultaneously. A color splitting system typically separates the output of the respective MLE into different color beams that are then transmitted, homogenized, aperatured and imaged onto the respective LV""s. The output of these LV""s is then spatially superimposed and projected onto a distant projection screen to form a color image of the LV""s. Typically three LV""s (see U.S. Pat. No. 5,098,184) are used, one for each color band. PLE""s that use multiple LV""s achieve in general greater light output for a given source S but also require typically larger and heavier PLE. Despite the increase in throughput efficiency TE these PLE typically are designed to be somewhat xc3xa9tendue limited and therefore have a lower delivery efficiency than possible with this invention. Other types of prior art PLE combine the output of multiple MLE""s into one integrator rod to achieve higher total system output, but not without a decrease in overall delivery efficiency.
The primary usage""s of LG""s in prior art, PLE""s is that of a Symmetric Beam Transformer (SBT), i.e. a system that has an axis symmetric beam reformatting behavior or that of a remote energy delivery system connecting a respective MLE to a projection system. For example, single channel LG""s made from straight, cladded or un-cladded (polished) rectangular rods or hollow reflective tubes are often used for beam intensity homogenization and to create a well defined emission aperture. Fiber bundles are sometimes used as LG for remote energy delivery.
U.S. Pat. No. 5,159,485 to Nelson (1992) describe a PLE that has incorporates an ABTLE. However, this design uses a lens based MLE resulting in a low delivery efficiency and the ABT has a low xc3xa9tendue efficiency.
Likewise, material processing applications of light typically require a minimum intensity and greater than minimum energy levels of illumination light in a specific wavelength interval to accomplish a desired light facilitated material process in a satisfactory processing time interval. Low power material processing examples of volume absorption systems are light curing of epoxy, soldering with light, marking with light, local chemical reaction control with light, photo dynamic therapy of tumors, etc. The efficiency of a given LE is often a major factor in deciding if only a laser or also a LG coupled, incoherent source can be used to accomplish the desired function in a cost effective manner. Further, the beam reformatting and delivery efficiency limits of the LE often determines the size of the target area/volume that can satisfactorily be exposed with light. Given the inherent xc3xa9tendue inefficiencies or design restrictions discussed above and below for the prior art LGLE""s, the cost of such a system may be much higher than the market can bear thus limiting the market penetration of such technologies.
Some material processing functions like Photo Dynamic Therapy (PDT) for light facilitated treatment of biological tumors or Photo Dynamic Diagnostic (PDD) methods can often use only a relatively narrow spectral energy band of a broad band source. If only the usable spectrum is delivered to the respective target location (for example, tissue to be illuminated), much of the generated optical source energy is typically wasted. In order to improve the delivery efficiency DE of useful light, fluorescence conversion methods are often being investigated. A dye laser is a typical example of an energy (fluorescence) shifting device that transforms a shorter wavelength pump wavelength into a longer frequency lasing (fluorescing) wavelength. However, it is often desirable to find a lower cost alternative to this solution. If a suitable fluorescent material is illuminated by light delivered from a first LE, the converted light escapes the fluorescing medium in all directions. The fluorescing volume FVS of the illuminated fluorescing material forms effectively a secondary source Sxe2x80x2 whose output needs to be collected and delivered to a target surface/volume T where it can be utilized. Again, prior art LE""s are not optimized to efficiently collect and deliver such spectrally shifted secondary sources. This reduces the practical usefulness of fluorescence conversion of incoherent light sources for many applications.
It is therefore an object of this invention to provide a method for designing delivery efficient LE""s for a broad range of xc3xa9tendue limited targets T.
It is another object of this invention to provide a method for designing xc3xa9tendue efficient and/or throughput efficient MLE""s.
It is still another object of this invention to provide a method for manufacturing color reformatting MLE""s.
It is a further object of this invention to provide a method for designing delivery efficient LGLE""s and ABTLE.
It is still another object of this invention to provide manufacturing methods for building matched LG""s and ABT""s with special input and output preparations and/or auxiliary optics to improve the throughput efficiency and/or delivery efficiency of a LE.
It is still a further object of this invention to provide improved cost/performance ratio of LE""s for given primary and/or intermediate target demands.
It is still a further object of this invention to provide improved PLE""s and new types of projection display systems.
It is still another object of this invention to provide a more flexible designs for automotive head light styling and remote industrial illumination systems.
It is still a further object of this invention to provide efficient fluorescence converting LE""s and lamps.
It is another object of this invention to provide efficient methods for color reformatting a light beam.
It as an still another object of this invention to provide LE""s that can be efficiently used in light facilitated material processing applications.
It is still a further object of this invention to change the manufacturing of related component to improve their usability for manufacturing high efficiency LE""s.
It is still another object of this invention to provide methods for reducing the size of related components while maximizing the delivery efficiency of a related LE
It is still a further object of this invention to provide a method for estimating the maximum achievable collection efficiency for a given source.
It is further object of this invention to provide a method for determining a minimal xc3xa9tendue surface of a concentrating light beam.
The delivery efficiency of a LE for a given, spatial extended emission source S and a given, remote illumination target T with respective spatial and angular dependent emission functions is improved by providing means for more xc3xa9tendue efficiently matching the optical properties of the source to the needs of the target and by providing optional means for spatial, angular and spectral beam reformatting.
Prior art LE""s are built with either non-imaging, high collection efficiency type, or imaging, but low collection efficiency type MLE""s. The present invention encompasses the design, manufacturing and use of imaging and more collection efficient type MLE""S for building more efficient LE""s for xc3xa9tendue limited target illumination. These preferred MLE""s achieve a much more xc3xa9tendue efficient 4xcfx80-steradian - greater than ≈xcfx80/2 solid angle conversion and allow generating a more usable exit beam for a wide range of target illumination applications. Further, prior art beam reformatting of the output of a MLE is accomplished with Symmetric Beam Transformers (SBT""s) or with low xc3xa9tendue efficient Anamorphic Beam Transformers (ABT""s), i.e. optical coupling system which have a different magnification in two orthogonal image directions. This invention describes the design and use of xc3xa9tendue an efficient ABT to increase the delivery efficiency of LE""s by reformatting the asymmetrical output beams of preferred types of MLE""s in an xc3xa9tendue efficient and/or delivery efficient manner. Additionally, various applications of these basic building blocks are discussed for building LGLE, PLE, fluorescence conversion LE and other types of LE. Numerical methods for characterizing and optimizing the respective components are discussed as well.
The preferred MLE is comprised of a reflective CCS and a reflective Retro Reflection System (RRS) having at least one exit port. The RRS collects less than 50% of the light emitted by the source S and either focussed it back into the original emission region or focussed it to a region nearby that has a small offset distance related to the width of the emission region and/or its enclosing envelope. The RRS operates as an image inverting, substantially non-magnifying, imaging system. Thus the source S together with the RRS forms an effective retro reflection source that emits typically in less than 2xcfx80-steradian and its respective emission region occupies either the same or about twice the volume of the source S. The respective CCS collects the light emitted by such a retro reflection source and concentrates into a secondary emission volume EVSxe2x80x2, thus forming effectively an xc3xa9tendue efficiently magnified secondary source Sxe2x80x2 with a respective smaller emission solid angle.
The beam exiting such a preferred type of MLE through the respective exit port(s) of the RRS, has a similar and magnified spatial intensity characteristic (quasi-imaging) to the emission region of the respective source S, and typically has an axial asymmetrical, angular dependent energy density distribution. Both the angular and spatial characteristics of the source S and secondary source Sxe2x80x2 are substantially xc3xa9tendue efficiently related and the total output efficiency of the MLE is close to the total light emitted by the source S.
The RRS system also provides an option for xc3xa9tendue efficient color reformatting by allowing about 50% of the emitted energy to interact one more time with the emission region of the source S. This effectively doubles the optical path length for gas discharge sources. Such light-material interactions can produce direct or indirect wavelength (primarily fluorescence and heating) conversion effects for some types of lamps and thus generate a MLE exit beam that has a different spectral intensity distribution than the same source has alone. Also, since the source S is now blocking some of the light delivery, its cross sectional area perpendicular to the CCS system axis becomes now important. This leads to an opportunity for further component manufacturing changes, which, in combination with the MLE deliver even more usable light.
The minimal xc3xa9tendue of a beam, collected at its minimal xc3xa9tendue surface is typically much smaller compared to prior art systems which have a comparable collection and concentration ability. This typically leads to smaller beam waists near the respective focal point and thus to more effective energy coupling to xc3xa9tendue limited targets.
Since the emission source Sxe2x80x2 has typically angular and spatial axial asymmetric characteristics which are xc3xa9tendue efficiently related, the preferred xc3xa9tendue efficient anamorphic beam reformatting with an ABT results effectively in a larger input port collection aperture for a given output ports emission aperture of the respective ABT. This increased design freedom in turn allows optimizing the respective delivery efficiency by trading the extend of the collection aperture with the extend of the collection solid angle of the MLE, thus allowing to optimally match the given spectral dependent, spatial extend of the emission region and of its emission angular extend with the collection aperture (size and shape) and collection solid angle demands.
Additionally since many types of emission source have a larger spatial extend for broad band emissions, the imaging type preferred MLE in combination with the increased collection aperture of ABT""s allows to typically collect a more broad band spectrum from a given source which, in combination with the RRS discussed above, further aids in the color reformatting of the source.
Asymmetrically tapered hollow or solid LG""s are often used as low cost ABT system that increase the delivery efficiency over prior art. Also special, high efficiency type LG with different input and output cross sectional shapes can be used for efficient spatial beam reformatting. Optionally an ABT can be used to first quasi-symmetrisize an asymmetric input beam first before further reshaping its beam cross section to a more usable shape. Often such ABT can also provide simultaneously a spatial beam intensity homogenization, which helps in increasing the delivery efficiency for PLE type applications. The combination of auxiliary optic with the ABT can aid in the design and optimization of constrained LE design tasks.
Auxiliary retro-reflectors can be used to further increase the collection efficiency and to aid in the color reformatting. Ideally for a given target, the lamp used for such a MLE is different than that used for prior art LE due to the multiple interaction of the light with the emission region and/or due to the higher xc3xa9tendue efficiency of the MLE and matched ABT""s. Special manufacturing features are discussed for allowing to maximize the delivery efficiency for size/height constraint CCS and RRS. Typically the respective MLE occupies a smaller volume than a prior art MLE producing the same output divergence and having the same height.
The combination of the MLE and the ABT allows the use of either more extended emission regions for given size targets or shrinkage of the system size. When such designs are optimized in this invention for Projection Light Engines (PLE) or fiber optic illumination systems this, brighter outputs and or lower cost system or system size for the same output level generally result.